I think with the bigger (Japanese) manufacturers they have a UK importer, dealers put their order in for the year, generally looking to get first delivery ready for March and the bikes get shipped in one go for the whole year? Any bikes left over, not taken by dealers are snapped up later in the year by dealers requiring more than their allocation.
With European, particularly Italian a lot of dealers order direct from the factory, the factory aren’t large enough to run production of multiple models simultaneously so first two weeks of a month they might be building Multistradas, next two might be scramblers and so on, so not all bikes are available at the same time.
I think that’s how it works, that’s what a dealer told me about MV anyways?